The Zombie Slayer utility was written after the release of the BB10 beta 4, where apps that crash may not exit fully. These "zombie" apps no longer have visible windows, and cannot be launched again until the device is rebooted!
When your unsigned app's icon stays "ghosted" (dimmed), run Zombie Slayer and it should allow you to select your app in the list, then tap Slay. A "SIGHUP" (kill) signal is sent to the app, which should generally terminate at that point.
You can also leave Zombie Slayer running and hit Refresh to update the list as needed. It does not yet scan automatically for active apps.
If you don't have Zombie Slayer yet, download it here.
Unfortunately we can't deliver this as a signed app, or it wouldn't be able to perform its function. This means you need to edit the MANIFEST.MF file in the .bar file to change the Package-Author and Package-Author-Id fields to match those in your debug token file. As a developer, you probably also have those values in your bar-descriptor.xml file as the <author> and <authorId> fields.
Use any "zip" program to extract the files, edit the MANIFEST.MF file to replace those two fields with your own values, and then re-zip the .bar file. You can now install it using blackberry-deploy or your usual means.
The Zombie Slayer was written in Python using an unreleased version of the BlackBerry-Tart package, which is a light-weight alternative to the original BlackBerry-Py concept. BlackBerry-Tart involves a small C++ application launcher which runs a basic Cascades app with a QML-based user interface, and connects it to a Python interpreter running in a separate thread through a simple JSON-based message passing mechanism. The result is you can write apps with little or no knowledge of C++, leveraging your existing Python experience.
If you don't already know Python: it's considered by many to be one of the easiest to learn modern programming languages. When used along with QML, Python makes writing Cascades apps even easier, and far more fun, and has hundreds of additional open source libraries you can integrate.
To learn more about BB-Tart, check out the resources list at the BlackBerry-Py site.
If you have suggestions or comments, please tweet to @BBPyProject.